Radial blower, especially for oil burners

ABSTRACT

A radial blade fan for use in connection with burners, in which a fan rotor is surrounded by a volute casing so as to form a gap therewith and has a blade exit angle of at least 90* while the volute housing has an inlet nozzle, said nozzle and the axis of said rotor being so located relative to each other that at least portions thereof are eccentrically located with regard to each other. The said volute or spiral housing has a sharp bend in the region of the beginning point of the volute or spiral from which departs on the one side the volute or spiral and on the other side a transition or connecting piece to the fan outlet.

Unlted States Patent 1 1 1 1 3,824,028 Zenkner et al. July 16, 1974 [54]RADIAL BLOWER, ESPECIALLY FOR OIL 820,398 5/1906 Davidson 415/204BURNERS 820,399 5/1906 Davidson 415/204 2,164,869 7/1939 Brady, Jr.415/53 [75] Inventors: K t n mg Franz 2,290,423 7/1942 Funk 415/206Kozel, Lippstadt; Heike Thomsen, 2,291,138 7/1942 Blom .1 415/53Schleswig, all of Germany 2,951,630 9/1960 Murphy 415/182 3,209,98910/1965 Eck 415/54 Asslgneel Punk Gmbli Apparatebau 3,407,995 10/1968Kinsworthy.. 415/204 garm te hm E r r 3,415,443 12/1968 Glucksman 415/54many FOREIGN PATENTS OR APPLICATIONS [22] Wed: 1971 139,678 12/1934Austria 415/204 [21] Appl. No.: 198,294

Primary ExaminerHenry F. Raduazo Related Apphcatlon Data Attorney,Agent, or FirmWalter Becker [63] Continuation-impart of Ser. No.874,756, Nov. 7,

9 l 69, abandoned [57] A S RAC [30] Foreign Application Priority Data Aradial blade fan for use in connection with burners, Nov. 7, 1968Germany 1807385 in which a fan rotor is Surrounded by a volute casing soas to form a gap therewith and has a blade exit 52 us. 01 415/53,415/182, 415/206, angle of at least while the volute housing has an 4 52 9 C inlet nozzle, said nozzle and the axis of said rotor 51 110.121.F04d 17/08, F04d 29/46 being S9 located relative to each other that atleast 5 Field f Search 53 54 1 2 219 C, portions thereof areeccentrically located with regard 41 204 20 to each other. The saidvolute or spiral housing has a sharp bend in the region of the beginningpoint of the 56] References Cited volute or spiral from which departs onthe one side the UNITED STATES PATENTS volute or spiral and on the otherside a transition or connecting piece to the fan outlet. 801,304 10/1905Davldson 415/204 820,397 5/1906 Davidson 415/54 5 Claims, 13 DrawingFigures 52 A :i 1 a 55 1\ 12 c 12 fi Ho 1 L. l

57 \J 4 54 O I H I! c Q, I 270 I PATENTEDJUUBISH sum 1 or 3 FIG- IPATENTEDJULI sum 3 3, 24,02

FIG -9 F IG- IO FIG-8 32d 32b 34c 2. 4

PATENTEDJUL 1 51m SHEET 3 (IF 3 FIG. [3

RADIAL BLOWER, ESPECIALLY FOR OIL BURNERS This is a continuation-in-partof co-pending application Ser. No. 874,756- Zenkner et al., filed Nov.7, 1969 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to a radial fan for conveying combustion air in burnerscomprising in combination a rotor or impeller with a blade exit angle ofat least 90 and a spiral casing or housing with a lateral inlet nozzle,whereby the beginning of the spiral of the housing lies in the area ofthe outlet i.e., the area in which the air leaves the impeller thespiral thereby embracing the periphery of the rotor along a distancewhich corresponds to an angle at the center of at least 270".

2. Prior Art Known radial blade fans of the kind here in question, forinstance when used in connection with a burner, have a pressure volumerate of fluid flow characteristic curve which has certain drawbacks andcorresponds approximatively to the characteristic curve A in FIG. 1. Inpractice, there is used just the descending branch of the characteristiccurve. More specifically, if in a burner installation comprising a fanof the above kind the resistance to flow changes, for instance becauseof a fouled filter, deposits of dust or carbon or also as a result ofpressure shocks when starting up or the like, the volumetric rate offluid flow falls very considerably, a very undesirable feature from thepoint of view of burner operation. In this respect radial blade fanshaving blade exit angles less than 90 have a more favorablecharacteristic. With decreasing blade exit angles the shape of thecharacteristic curve improves, but at the same time the pressure gaincoeffiecient is reduced and a fan of larger size must be provided. Thisis undesirable.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide a radial blade fan of the above specified kind which, despiterelatively small dimensions, has a steep characteristic coupled with ahigh pressure gain when the volumetric rate of fluid flow is low.

Another object of the present invention consists in to provide a fan ofthe above described general character with which the housing on the oneside and the inlet nozzle on the other side present the combination ofthe following features:

a. between the beginning point of the spiral of the housing whichcorresponds to the point of the narrowest distance between the housingand the pe riphery of the impeller on the one side and the blower or fanoutlet on the other side there is provided as transition and connectingpiece a housing portion, whereby the distance between the said housingportion and the periphery of the impeller is, as seen over its lengthand in direction towards the blower or fan outlet, either constant orincreasserving as transition or connecting piece to the blower outlethas the shape of a sharp bend;

. the beginning point of the spiral of the housing corresponding to theplace of the narrowest or smallest distance between the housing and theperiphery of the impeller extends only about a point-like distance asseen in the direction of the impeller and is situated at such a distancefrom the periphery of the impeller that at this point the space betweenthe housing and the impeller is not sealed and these parts are not closeto one another, so that air can flow through the space between thecasing and the periphery of the impeller, whereby this point of thenarrowest distance between the housing and the impeller in associationand co-operation with the housing wall portion serving as transition andconnecting piece serves the purpose of diverting a part of the airexiting from the impeller and reintroducing it into the interior of theimpeller by passing it through the impeller blading;

d. the periphery of the inlet nozzle so differs at certain locations orpoints from the circle described with the radius of the nozzle about theimpeller axis that there results a difference of at least 2 percent withrespect to the cross-sectional surface enclosed by the said circle.

Yet another object of the present invention consists in to provide a fanof the above mentioned type in which a steep increase of the pressure isobtained with decreasing volume rates and with which, therefore, evenwith great and considerable pressure variations no volume variations atall or only small volume variations can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will nowbe described, by way of example, with reference to the accompanyingdrawings. In the drawings:

FIG. 1 illustrates a pressure volume rate of flow characteristic curveof a conventional fan and a corresponding curve of a fan according tothe invention cooperating with an oil burner.

FIG. 2 is a side view of the casing of a fan according to the invention,

FIGS. 3 and 4 show two alternative embodiments of the fan according tothe invention each in a vertically sectioned schematical side view,

FIG. 5 is a fragmentary side view of an embodiment of an inlet nozzleformed with a cross sectional constriction on one side.

FIG. 6 is a section taken on the line VIVI in FIG.

FIG. 7 shows the casing of a fan according to the invention having aneccentrically disposed inlet nozzle in a schematical and sectionalfrontview,

FIG. 8 is a representation of the gap between the fan wheel and theinternal wall of the casing and of a special nose at the beginning ofthe casing, i.e., where the volute casing is narrowest on a greaterscale,

FIG. 9 is a modified form of construction of the initial area of thevolute casing in the same manner of representation as in FIG. 8, and

FIG. 10 is another modification of the initial section of the volutecasing in which this initial region is preceded by a wedge elementdefining a by-pass channel.

FIG. 11 shows the inlet nozzle in the structure of FIG. 3.

FIGS. 12 and 13 are cross sections on lines 12-l2 and I313,respectively, of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingsin detail, FIG. 1 shows the pressure volume rate of flow characteristiccurve A of a fan according to the present invention with forwardlycurved blades co-operating with a burner. B is the correspondingcharacteristic curve of a conventional fan of the same diameter androtating at the same speed. It will be readily seen that with the fanaccording to the invention substantially higher pressure heads can beobtained at low volume rates of fluid flow.

Consequently, in its use with a burner a fan according to the inventionis capable of providing better starting conditions. Therefore, as willbe understood from FIG. 1, with the fan according to the invention,there is obtained a steep characteristic curve and high pressure figuresalso in the range of smaller output volume figures, the pressure of themedium increases, therefore, rapidly or steeply when the volume rates offlow decrease. Since with burners it is desirable that with greatpressure variations no output volume variations at all or only smalloutput volume variations should occur, in order not to change or alterthe outcome of results of the combustion operation, the invention isespecially suited for the use with burners, all the more as the aboverequirement is of great importance with burners just nowadays as theboiler resistances become greater and greater.

In FIG. 2 shows schematically the casing of a fan according to theinvention in side view. 10a is the initial or beginning section of-thevolute casing, whereas 10b is the blower outlet. The volute casing orspiral housing has means defining an inlet nozzle which is marked with11 in FIGS. 2 and 6. In this case, the inlet has a circular crosssection and its axis 110 is eccentrically displaced by an amount 13 inrelation to the position shown in dotted lines of an imaginary inletnozzle of same magnitude disposed coaxially with the fan wheel axis 11aand having the same likewise circular cross section. The eccentricdisposition of the inlet nozzle 11 with cross-circular section and withrespect to impeller or fan wheel axis results in an overlapping of thesurface of the real nozzle arranged eccentrically and of the surface ofthe imaginary centric nozzle by a certain amount. This amount, by whichthe free cross sectional area of the inlet nozzle differs from theareaof the circle described with the radius of the nozzle around the axis ofthe rotor is so chosen that there results a differ ence of at least 2percent. This difference is shown in FIG. 2 as shaded surface and ismarked with f.

FIG. 5 illustrates another embodiment of an inlet nozzle according tothe invention. This inlet nozzle is here arranged centrically andgenerally indicated by reference number 20. At 200 there are inwardlobes so that the inlet nozzle is constricted and constructed by havingthe wall surrounding the opening somewhat flattened. The constrictionamounts to at least 2 percent of the total cross section of the circularnozzle. Therefore. the difference between the real and effective openingof the nozzle, the cross-section of which is smaller by the flattenedportion, and the cross-section of the circle described around the axisof the rotor with the radius of the nozzle amounts to 2 percent or more.The direction, by which the nozzle is staggered with respect to thecircle described with the radius of the nozzle around the axis of therotor, may be charged within some limits, the nozzle and itseccentricity can be, therefore, adjusted somewhat in order to adapt thearrangement to different conditions. It is preferred, however, toprovide an eccentricity of the nozzle within the area of the firstquadrant so that the nozzle is eccentric towards the pressure side.Naturally, the constriction need not be shaped as shown in the drawings.It is quite arbitrary. For example, an inlet nozzle of basicallycircular cross section might be flattened on one side.

In FIG. 7, the arrangement according to FIG. 2 fan and eccentricallyarranged inlet nozzle is shown in a schematical and sectional frontview. The rotor is marked with 65, 66 is the outline of the casing, 11is the inlet nozzle. 67 is the inner diameter of the blading, and 68 isthe part of the eccentrically arranged inlet nozzle which is farthestoutside the inner diameter of the blad- By the above measures andfeatures the fluid medium or at least a part of this medium is forcedrepeatedly or for several times through the blading which fact explainswhy the pressure increases with small volume rates of flow and thecharacteristic curve is so steep. To this purpose there serves also thenew shape of the volute casing and especially of the initial area ofthis casing. As can be taken from the drawings and especially from FIGS.2 and 4, with the volute casing of the arrangement according to theinvention the beginning of the spiral of the casing lies in the area ofthe outlet and embraces the periphery of the rotor along a distancewhich corresponds to an angle at the center of at least 270 deg. Asshown in FIG. 11, the inlet opening is offset relative to the impellerby the amount of the displacement of its axis 11 from the axis 13 of theimpeller, so that the side wall covers the circumferential portion ofthe impeller ahead of the outlet and the opening exposes the oppositecircumferential portion of the impeller. The inlet nozzle is formed by aconverging portion extending inwardly toward the impeller and a flat,peripheral flange 15 held on the side wall by lugs 16. With thearrangement according to FIG. 3 there is provided between the beginningof the spiral of the casing corresponding to the point 50 of narrowestdistance between the housing or casing 51 and the periphery of the rotor52 on the one side and the fan or blower outlet 53 on the other side astransition and connecting piece a housing portion 54 of the housing thedistance of which to the periphery of the rotor increases as seen indirection towards the blower or fan outlet according to the arrow 55,said housing portion being allotted or associated to an are a along theperiphery of the impeller which corresponds to a small arc alpha at thecenter, for instance, of 5 deg. The transition between the beginning ofthe spiral of the housing at the point 50 and the housing portion 54serving as transition or connecting piece to the blower or fan outlethas the shape of a sharp bend. This point 50 which at the same timerepresents the beginning of the spiral and is situated at the smallestdistance to the periphery of the impeller so that it corresponds to thenarrowest interspace between the impeller and the periphery of the rotorextends only about a point-like distance as seen in the direction of theimpeller and thereby faces only a point on the periphery of the impellerand does not cover an are of this impeller periphery. The distance ofthis point 50 to the periphery of the impeller is so great that at thisplace the space between the housing and the impeller is not sealed andthese parts are not close to one another so that medium can pass betweenthe periphery of the rotor and the housing from the initial or beginningarea of the housing. Due to such a shape of the casing and of theimpeller and due to the eccentrical position of the nozzle there takesbirth a vortex core which is arranged approximatively in the area of theperiphery of the impeller and serves together with the point 50 of thehousing closest to the periphery of the impeller and with the housingportion 54 serving as transition and connecting piece to divert a partof the air exiting from the impeller according to the arrows 56 andreintroduce it into the interior of the impeller and let it flow fromthere to the exterior by passing it through the impeller blading. Due tothe fact that the air flow is repeatedly passed through the blading ofthe impeller, the interchange of energy between the blading and the airflow is substantially enhanced and the blading imparts to the air flowadditional energy. Due to the fact that the air can leave the impelleralready directly after the point of narrowest distance between thehousing and the impeller, pressure is built up in the diffusor-likeinterspace between the housing and the periphery of the impeller at anearly stage, namely directly after this point of narrowest distance. Bythese means there is obtained with the blower or fan according to theinvention such a high pressure figure. In the throttled stage of the fanthe vortex core is at a greater distance from the point of narrowestdistance between the housing and the periphery of the rotor than in theunthrottled stage, since upon throttling the vortex core travels awayfrom the point of narrowest distance, but remains within the area of theperiphery of the impeller or rotor. It results therefrom that with smallvolume rates of flow there is branched off a greater amount of air whichis then reintroduced into the impeller for repeating the interchange ofenergy. Due to the fact that the vortex core more and more floatstowards the fan outlet upon decreasing of the throttling, the distancebetween the point of narrowest distance and the vortex core becomessmaller when the fan is not throttled so that the amount of issuing airwhich is branched off by the point 50 of narrowest distance and theadjoining housing portion 54 and which thereafter is reintroduced intothe impeller becomes smaller and smaller in relation to the total amountof issuing air so that, as a further consequence, the pressure figuredecreases with increasing volume rate of flow.

Whereas with the arrangement according to FIG. 3 the portion 54 of thewall of the casing has an indent or notch 57 which promotes the tendencythat a portion of the medium to be conveyed passes several times throughthe impeller so that the pressure substantially increases with smallervolume rates of flow, with the arrangement according to FIG. 4 such anindent or notch is no more present. Here, the transition and connectingpiece 60 between the point 61 of the narrowest distance between thevolute casing 62 and the periphery of the rotor 63 and the outlet area64 is constructed without any indent or notch, whereby this point 61 ofnarrowest distance represents also a transition in the shape of a sharpbend and with point-like extension and whereby the diffuser-likeenlargement of the interspace between the volute casing and theperiphery of the impeller begins at this point of narrowest distancewhich covers or screens only a point of the periphery of the impeller.With this embodiment also the air flow is the same as described abovewith reference to FIG. 1.

In FIG. 8 there is shown schematically an embodiment of the initialregion of the volute casing according to the invention. 31 is theimpeller or rotor and 30 is a nose which defines the gap 32 between thecasing or housing and the impeller at the beginning of the casing. Aswill be understood from the drawings, the gap 32 at the initial area321; is concentric with the fan wheel along an arc corresponding to anangle at the center of at least 5, said gap area 32b having constantwidth. In the region 32b the gap merges into the usual scroll shapewhich is not here represented.

At the point 320, therefore, the wall of the casing which embraces theimpeller makes a sharp bend, the transition between the wall portions32a and 32e takes place as a sharp bend as at 32c, whereby this point32c and the area 32d lie nearest to the periphery of the impeller. FIG.9 shows a somewhat modified form of construction of the initial sectionof the casing. 33 is the nose which defines a channel 34 of which theend portion is marked with 340 and of which the narrowest portion ismarked with 34b. The channel has a constriction at 34b and then widensagain, as indicated at 34a. The angle at the center, which correspondsto the initial portion 340 up to the constriction 34b, may amount up to10 deg.

FIG. 10 is yet another modification in which the nose defining the gapat the initial region is marked with 40. 41 is the beginning or initialregion of the gap comprising an initially concentric portion 41b merginginto a widening portion at 41a, whereby these two portions are separatedby the bend 41c. In the prolonged axis of the nose there is provided awedge element 42 which forms a gap 43 between itself and the fan wheel31 as well as a b'y-pass channel 44. This form of conor repeatedinterchange of energy. Conveniently, the wedge element 42 is pivotablymounted on a shaft represented by its axis 45 to permit the crosssections of the gap 43 and of the by-pass channel 44 to be varied, forexample, to be varied in directions contrary to one another in orderthat the characteristic curve of the fan be adjusted accordingly.

The proposed construction of the fan is not limited to the use inconnection with burners although this is the preferred use.

Although our invention has been illustrated and described with referenceto the preferred embodiments thereof, we wish to have it understood thatit is in no way limited to the details of such embodiments, but iscapable of numerous modifications within the scope of the appendedclaims.

Having thus fully disclosed our invention, what we claim is:

l. A radial fan for conveying air comprising a rotor impeller havingblades extending approximately radially of the rotor and a casing havingaxially spaced sides with a lateral inlet in one side and a spiral wallextending approximately 270 about said impeller and integral, parallelcontinuations of the ends of said spiral wall forming parallel walls ofan outlet of said casing, said spiral wall having its first end spacedfrom said impeller with the spacing of said spiral wall from saidimpeller increasing toward the other end, said first end being joined tothe corresponding parallel wall by a transition portion which is concavetoward the opposite parallel wall and is joined to the first end of saidspiral wall by an integral sharp bend forming a projection directed in adirection opposite to the direction of rotation of said impeller, sothat the air from said impeller blades is divided into a main currentout from said impeller discharged through said outlet, and anothercurrent deflected by said concave transition portion toward theperiphery of said impeller into said blades, said inlet being offsetrelative to the axis of said impeller so that said side wall covers onecircumferential portion of said impeller on one side and the inletopening exposes a circumferential portion of said impeller on theopposite'side and said inlet has a converging nozzle projecting inwardlyfrom said side wall toward said impeller.

2. The radial fan in combination according to claim impeller.

5. The radial fan in combination according to claim 4, wherein the saidinlet nozzle is staggered with respect to an exactly centrally arrangednozzle'in direction towards the region in which the air leaves theimpeller.

1. A radial fan for conveying air comprising a rotor impeller havingblades extending approximately radially of the rotor and a casing havingaxially spaced sides with a lateral inlet in one side and a spiral wallextending approximately 270* about said impeller and integral, parallelcontinuations of the ends of said spiral wall forming parallel walls ofan outlet of said casing, said spiral wall having its first end spacedfrom said impeller with the spacing of said spiral wall from saidimpeller increasing toward the other end, said first end being joined tothe corresponding parallel wall by a transition portion which is concavetoward the opposite parallel wall and is joined to the first end of saidspiral wall by an integral sharp bend forming a projection directed in adirection opposite to the direction of rotation of said impeller, sothat the air from said impeller blades is divided into a main currentout from said impeller discharged through said outlet, and anothercurrent deflected by said concave transition portion toward theperiphery of said impeller into said blades, said inlet being offsetrelative to the axis of said impeller so that said side wall covers onecircumferential portion of said impeller on one side and the inletopening exposes a circumferential portion of said impeller on theopposite side and said inlet has a converging nozzle projecting inwardlyfrom said side wall toward said impeller.
 2. The radial fan incombination according to claim 1, wherein before the beginning of thespiral of the housing as seen in direction towards the fan outlet thereis arranged a wedge-shaped nose defining together with the housing wallportion serving as transition and connecting piece a by-pass channel. 3.The radial fan in combination according to claim 2, wherein the saidwedge-shaped nose is mounted pivotably about an axis parallel to theimpeller axis.
 4. The radial fan in combination according to claim 1,wherein the said inlet nozzle is circular in cross-section and isarranged eccentrically to the axis of the impeller.
 5. The radial fan incombination according to claim 4, wherein the said inlet nozzle isstaggered with respect to an exactly centrally arranged nozzle indirection towards the region in which the air leaves the impeller.